Several levels of fan construction exist in the petrochemical industry. API, ASME and ISO have all generated specifications for these applications. Fired heaters and sulfur recovery units, along with their associated combustion and pollution control systems, make up a large part of the refinery chemical process applications. All of these fans are smaller versions of traditional mechanical draft equipment, but they require special bearings, couplings and dual-drive systems. Complete seal welding and extreme environment coatings are usually required. NYB can offer designs to complete all of these requirements.